I vote for Mt. Tam double. It's always nice when you don't have to travel too far.

+1.... but sign up fast. It could fill up, if it hasn't already.

As for back to back doubles, you should be fine as long as you're not struggling just to finish a double. I did Central Coast and Davis on b2b weekends with no problems. 6 days of recovery is plenty. My Wed. night mtb races really suffered though....